The present invention relates to a feed roller for use in feeding timber, the feed roller comprising a body having disposed around its periphery friction elements comprising anti-slip elements for improving the engagement between the feed roller and the log, the friction element comprising at least one coupling means for arrangement thereof to the body, and a transfer means for transferring the rotational motion of the feed roller to the friction element.
Feed rollers of this kind are generally used in harvesters. In this context, a feed roller refers to a roller directing both a pulling and pushing motion to the log e.g. in such a harvester. Consequently, a drive wheel, feed wheel or roller wheel may be involved. Generally known feed roller techniques include fixed wheels mostly made of steel, and wheels containing different kind of drive elements and rubber mixtures.
Fixed rollers used as feed rollers usually consist of a cylinder and various almost immobile anti-slip elements attached thereto. These are easy to manufacture, but because of an unfavourable distribution of surface tension, they easily damage the surface of the log. With increasing mechanical harvesting, surface damage to the timber has become an increasingly important factor in the economic use of timber.
Feed rollers of this kind comprising anti-slip elements articulated to the feed roller are disclosed in publications EP 0 478 522 and Fl 54244, for example. To enable a small swinging motion of the anti-slip element, dampers made of a rubber material are disposed in connection with, preferably between, the anti-slip elements according to EP 0 478 522, for example.
However, previous solutions have drawbacks which have so far not been solved. Accordingly, the anti-slip elements of feed rollers have usually been arranged to follow the motion of the surface of the feed roller. This makes the anti-slip elements dig into the surface of the log being conveyed, causing unfavourable damage to the surface during harvesting.
Furthermore, providing the feed roller with rubber dampers causes problems as the dampers bind some of the feeding energy directed to the log by the feed roller, resulting in an increased need for feed force. Increased use of force, in turn, increases the surface pressure of the feed roller, causing unfavourable heating to the roller and its rubber coating. Heating of the roller, in turn, leads to changes in roller dimensions, causing inaccuracy to the measurement of the logs. Heating of the roller and the rubber, in particular, reduces the service life of rubber rollers. This results in impaired grip characteristics, and the roller coating has to be renewed repeatedly. Besides being expensive, such renewal of the coating causes unnecessary idle periods to valuable machinery.
FI54244 differs from other solutions in that the friction elements of the feed roller are arranged to swing along the surface of the fed timber. However, such articulation of the feed roller is structurally difficult to implement to ensure a sufficient strength.
It is an object of the present invention to eliminate prior art drawbacks and provide a completely new kind of solution providing better friction properties and a more even feeding motion that previously. It is a further object of the invention to provide a feed roller without harmful wear characteristics of rubber-coated wheels, resulting in longer maintenance intervals.
This object is achieved by the feed roller having the characteristics of the present invention as defined in the claims. To be more exact, the device of the present invention is mainly characterized in that preferably the periphery of the transfer means comprises lugs which are disposed in grooves at the bottom of the friction element.
The invention is based on the idea of avoiding the damaging impacts directed to the surface of a log and the abrasive motion caused by the anti-slip element to the surface when the feed roller rotates. This is accomplished by attaching the friction elements, provided with anti-slip elements, rotatably to the body so that as many anti-slip elements as possible are constantly in contact with the surface of the log. The abrasive motion can be further reduced by a mechanical coupling between the friction elements.
The turning of the friction element caused by the traction force of the log does not have to be limited or even necessarily dampened by e.g. rubber if the rotation axis of the swinging motion between the friction element and the body is placed preferably in the vicinity of that surface of the friction element which faces the log. In this case the friction element is immobile during feeding with respect to the surface of the log.
The structure of the feed roller according to the invention provides significant advantages. The arrangement of at least two arrays of anti-slip elements on the surface of the friction element enables a greater number of arrays of anti-slip elements than usual to be constantly in contact with the surface of the log. The anti-slip elements of the invention are also immobile with respect to the surface of the log when the feed roller is rotating, the entire surface of the friction element resting against the surface of the log. Similarly, the entire surface of the friction element is detached substantially simultaneously. This naturally provides a significant improvement compared with fixed anti-slip elements in a feed roller. In the most disadvantageous situation only one array of anti-slip elements is in contact with the surface of the log being conveyed, the anti-slip elements hitting and damaging the surface of the log. The present invention also avoids the penetration by the anti-slip elements of conventional feed rollers of the surface of the log during harvesting. This way excessive damage to the surface of the log can be avoided and consequently as high a market value for the timber as possible can be maintained.
With a significant friction element turning radius, the device of the invention provides a feed roller having an even surface pressure even at lumps and other roughness on the surface of the log.
The radius of the feed roller is always substantially constant, since the friction element of the invention does not have to be mobile in the direction of the radius of the feed roller. This allows measurement of various magnitudes, such as thickness, of the log from the control mechanisms of the feed rollers. This also provides a feed roller whose measurement accuracy shows no substantial variations caused by temperature changes.
Furthermore, the friction elements of the feed roller of the invention are more simple to repair, even by the user alone, resulting in significant savings in maintenance costs.